This application is one of a group of commonly assigned patent applications which include application Ser. No. 08/576,543 entitled xe2x80x9cAn Apparatus and Method for Emulsifying A Pressurized Multi-Component Liquidxe2x80x9d, in the name of L. K. Jameson et al.; and application Ser. No. 08/576,522 entitled xe2x80x9cUltrasonic Liquid Fuel Injection Apparatus and Methodxe2x80x9d, in the name of L. H. Gipson et al. The subject matter of each of these applications is hereby incorporated herein by this reference.
The present invention relates to an apparatus for injecting fuel into a combustion chamber and in particular to a unitized fuel injector for engines that use overhead cams to actuate the injectors.
Diesel engines for locomotives use unitized fuel injectors that are actuated by overhead cams. One such typical conventional unitized injector is schematically represented in FIG. 1 and is generally designated by the numeral 10. This unitized injector 10 includes a steel valve body 11 that is disposed in an injector nut 29. The steel valve body 11 houses a needle valve that can be biased in the valve""s closed position to prevent the injector from injecting fuel into one of the engine""s combustion chambers, which is generally designated by the numeral 20.
As shown in FIG. 1B, which depicts an expanded cross-sectional view of a portion of the steel valve body 11 of FIG. 1, the needle valve includes a conically shaped valve seat 12 that is defined in the hollowed interior of the valve body 11 and can be mated with and against a conically shaped tip 13 at one end of a needle 14. The hollowed interior of the valve body 11 further defines a fuel pathway 15 connecting to a fuel reservoir 16 and a discharge plenum 17, which is disposed downstream of the needle valve. Each of several exit channels 18 typically is connected to the discharge plenum 17 by an entrance orifice 19 and to the combustion chamber 20 by an exit orifice 21 at each opposite end of each exit channel 18. The needle valve controls whether fuel is permitted to flow from the storage reservoir 16 into the discharge plenum 17 and through the exit channels 18 into the combustion chamber 20.
The conically shaped tip 13 at one end of needle 14, which is housed in the hollowed interior of the valve body 11, is biased into sealing contact with valve seat 12 by a spring 22, which is housed in a cage 28 so as to be disposed to apply its biasing force against the opposite end of the needle 14 as shown in FIG. 1. A fuel pump 23 is disposed above the spring-biased end of the needle 14 and in axial alignment with the needle 14. Another spring 24 biases a cam follower 25 that is disposed above and in axial alignment with each of the fuel pump 23 and the spring-biased end of the needle 14. The cam follower 25 engages the plunger 26 that produces the pump""s pumping action that forces pressurized fuel into the valve body 11 of the injector. An overhead cam 27 cyclically actuates the cam follower 25 to overcome the biasing force of spring 24 and press down on the plunger 26, which accordingly actuates the fuel pump 23. The fuel that is pumped into the valve body 11 via actuation of the pump 23 hydraulically lifts the conically shaped tip 13 of the needle 14 away from contact with the valve seat 12 and so opens the needle valve and forces a charge of fuel out of the exit orifices 21 of the injector 10 and into the combustion chamber 20 that is served by the injector.
However, the injector""s exit orifices can become fouled and thereby adversely affect the amount of fuel that is able to enter the combustion chamber. Moreover, improving the fuel efficiency of these engines is desirable as is reducing unwanted emissions from the combustion process performed by such engines.
The goal of achieving more efficient combustion, which increases power and reduces pollution from the combustion process, thereby improving the performance of injectors, has largely been sought to be accomplished by decreasing the size of the injector""s exit orifices and/or increasing the pressure of the liquid fuel supplied to the exit orifice. Each of these types of solutions aims to increase the velocity of the fuel that exits the orifices of the injector.
However, these solutions introduce problems of their own such as: the need to use exotic metals; lubricity problems; the need to micro inch finish moving parts; the need to contour internal fuel passages; high cost; and direct injection. For example, the reliance on smaller orifices means that the orifices are more easily fouled. The reliance on higher pressures in the range of 1500 bar to 2000 bar means that exotic metals must be used that are strong enough to withstand these pressures without contorting in a manner that changes the characteristics of the injector, if not destroying it altogether. Such exotic metals increase the cost of the injector. The higher pressures also create lubricity problems that cannot be solved by relying on additives in the fuel for lubrication of the injector""s moving parts. Other means of lubricity such as applying a micro inch finish on the moving metal parts is required at great expense. Such higher pressures also create wear problems in the internal passages of the injector that must be counteracted by contouring the passages, which requires machining that is costly to perform. These wear problems also erode the exit orifices, and such erosion changes the character of the injector""s plume over time and affects performance. Moreover, to achieve the higher pressures, the fuel pump must be localized with the injector for direct injection rather than disposed remotely from the injector.
Using ultrasonic energy to improve atomization of fuel injected into a combustion chamber is known, and advances in this field have been made as is evidenced by commonly owned U.S. Pat. Nos. 5,803,106; 5,868,153 and 6,053,424, which are hereby incorporated herein by this reference. These typically involve attaching an ultrasonic transducer on one end of an ultrasonic horn while the opposite end of the horn is immersed in the fuel in the vicinity of the injector""s exit orifices and caused to vibrate at ultrasonic frequencies. However, unitized fuel injectors cannot be fitted with such ultrasonic transducers because of the disposition of the fuel pump, cam follower and overhead cam in axial alignment with the needle.
Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In a presently preferred embodiment of the present invention, the standard unitized injector actuated by overhead cams is retrofitted by replacing the steel valve body with a valve body that is composed of ceramic material that is transparent to magnetic fields oscillating at ultrasonic frequencies. The ceramic material is harder and more wear resistant than the steel at the pressures involved.
The retrofitting of the valve body also includes replacing the steel needle with a needle that has an elongated portion that is composed of magnetostrictive material that is capable of responding mechanically to magnetic fields oscillating at ultrasonic frequencies. The portion of the ceramic valve body surrounding the magnetostrictive portion of the retrofitted needle is itself surrounded by a wire coil that is capable of inducing in the region occupied by the magnetostrictive portion of the needle a magnetic field that is oscillating at ultrasonic frequencies and thus causes the magnetostrictive portion to vibrate at ultrasonic frequencies. This vibration causes the tip of the needle, which is disposed in the liquid fuel near the entrance to the discharge plenum and the channels leading to the injector""s exit orifices, to vibrate at ultrasonic frequencies and therefore subjects the fuel to these ultrasonic vibrations. The ultrasonic stimulation of the fuel as it leaves the exit orifices permits the injector to achieve the desired performance while operating at lower pressures and using larger exit orifices than the conventional solutions that are aimed at increasing the velocity of the fuel exiting the injector.
In accordance with the present invention, a control is provided for actuation of the ultrasonically oscillating signal. The control is configured so that the actuation of the ultrasonically oscillating signal that is provided to the coil only occurs when the overhead cams are actuating the injector so as to allow fuel to flow through the injector and into the combustion chamber from the injector""s exit orifices. Thus, the control operates so that the ultrasonic vibration of the fuel only occurs when fuel is flowing through the injector and into the combustion chamber from the injector""s exit orifices. This control can include a sensor such as a pressure transducer that is disposed on the cam follower and includes a piezoelectric transducer that detects the pressure change indicating actuation of the follower by the cam.
Moreover, injectors can be made in accordance with the present invention as original equipment rather than as retrofits.